Gridview button with condition

[pikkas]

I have a gridview with 3 columns Name,Surname,Change(ButtonField column) which is populated from an SqlDataReader with the following code

SqlCommand sqlCommand = new SqlCommand("select * from Empl where userId ='" + userid + "'", sqlConnection);
            sqlConnection.Open();

            SqlDataReader reader = sqlCommand.ExecuteReader();

            GridView1.DataSource = reader;
            GridView1.DataBind();

In my database there are 4 columns UserId,Name,Surname,Change(bit). How can i show the button change only when Change(bit) column is true inside the database?